(Meth)acrylic acid is produced generally by introducing a (meth)acrylic acid-containing gas obtained by vapor-phase contact oxidation reaction into a condensation tower or a collection tower to obtain an aqueous (meth)acrylic acid solution and further purifying the solution. An ester of (meth)acrylic acid is produced by esterifying purified (meth)acrylic acid or crude (meth)acrylic acid at proper timing and carrying out purifying based on the necessity. As a purification method of (meth)acrylic acid and/or an ester thereof (hereinafter, referred to as “(meth)acrylic acid and the like”), a method in which an aqueous solution of (meth)acrylic acid and the like is introducing into an azeotropic separation tower and is subjected to azeotropic distillation in the presence of an azeotropic solvent has been known well. However, (meth)acrylic acid or the like is very easily polymerized. Therefore, particularly in high temperature facilities such as an azeotropic separation tower and a distillation tower, a polymerization inhibitor to prevent the polymerization of (meth)acrylic acid and the like is employed.
It has been well known that a dialkyldithiocarbamic acid copper salt alone or in combination with another polymerization inhibitor is used as the polymerization inhibitor used in the production process for (meth)acrylic acid and the like, as disclosed in JP-A No. 2003-103155, JP-A No. 6-211735 and JP-A No. 9-95465.